1. Field of Invention
The present invention relates to a MEMS device with a deformation protection structure, a deformation protection structure for use in a MEMS device, and a method for manufacturing a MEMS device.
2. Description of Related Art
FIG. 1 shows a MEMS device disclosed in U.S. Pat. No. 4,901,570. As shown in FIG. 1, the MEMS device includes: a proof mass 11, a supporting substrate 12, cantilevers 13, a silicon nitride layer 14 formed on the surface of the proof mass 11 and the supporting substrate 12, and a bridge section 15. In normal operation, the MEMS device 10 generates signals by detecting a displacement of the proof mass 11, while for protecting the device from damage by abnormal operation (such as shock), the prior art limits the movement of the proof mass 11 in two ways: first, the bridge section 15 limits the rotation of the proof mass 11 and it also limits the out-of-plane movement of the proof mass 11 to some extent. Second, the cantilevers 13 which are fixed to the supporting substrate 12 by means of the silicon nitride layer 14, and higher than the proof mass 11 by a gap 16, limits the out-of-plane movement of the proof mass 11.
In this prior art, the proof mass 11 and the supporting substrate 12 are made by silicon while the cantilevers 13 are made by polysilicon. In other words, the MEMS device 10 has to be made before a metal interconnection process, because it uses the silicon substrate to form the proof mass 11 and the supporting substrate 12; thus, this prior art cannot be applied to a MEMS device which has a metal proof mass and a supporting silicon substrate under the proof mass. Moreover, this prior art has a drawback that the supporting substrate 12 needs to surround all outer sides of the proof mass 11 so that the cantilevers 13 fixed to the upper side of the supporting substrate 12 can surround the proof mass 11 to sufficiently limits the movement of the proof mass 11. Thus, the device requires a large area and is difficult to shrink.
FIG. 2 shows, by cross section view, a MEMS device 20 disclosed in U.S. Pat. No. 7,237,316. The MEMS device 20 is manufactured by the following steps: providing a silicon on insulator (SOI) wafer, and etching the glass plate 25 to define a proof mass 21, a stationary frame 22, and stoppers 23, etc. As shown in FIG. 2, in the MEMS device 20, the proof mass 21 and the stationary frame 22 are both made by etching the substrate. A gap 26 is formed between the stoppers 23 and the proof mass 21 by etching a part of an insulating layer 24; the dimension of the gap 26 is defined by the height of the insulating layer 24.
Similarly, this MEMS device 20 has to be made before the metal interconnection process, and therefore the prior art cannot be applied to a MEMS device which has a metal proof mass and a supporting silicon substrate under the proof mass. Also, the prior art has the same drawback that the supporting substrate 22 needs to surround all outer sides of the proof mass 21 so that the stoppers 23 fixed to the upper side of the supporting substrate 22 can surround the proof mass 21 to sufficiently limits the movement of the proof mass 21. Thus, the device requires a large area and is difficult to shrink.
In view of the above, the present invention proposes a MEMS device with a deformation protection structure, a deformation protection structure for use in a MEMS device, and a method for manufacturing a MEMS device, to overcome the drawback in the prior art.